Controlled delivery of immiscible materials into an aqueous system

ABSTRACT

Immiscible components are controllably released into aqueous systems by impregnating silica-silicate open cell foams with the immiscible components. As the silica-silicate foams are gradually dissolved, the immiscible components are released. Fragrance oils and dyes are particularly adaptable for use in the invention. In fact, silica-silicate foams impregnated with fragrance oils having polar functional groups, exhibit an unexpectedly slower rate of dissolution into aqueous environments and consequently, fragrance oils and dyes admixed therewith are released in aqueous systems over extended time periods.

This is a divisional application of co-pending application Ser. No.303,472, filed Sept. 18, 1981, now U.S. Pat. No. 4,440,542.

FIELD OF THE INVENTION

Materials normally insoluble and immiscible in aqueous systems may bereleased in a controlled manner into such systems by adsorbing andtrapping the materials on and into the interstices of a water-solubleinorganic foamed structure i.e., a silica-silicate foam. As the foamedstructure slowly dissolves into the aqueous environment, the absorbedand trapped materials are concurrently released.

BACKGROUND OF THE INVENTION

In the treatment of aqueous systems with sanitizing and/orbacteriostatic, or surface active agents, it is very often desirable,especially in the consumer products markets, to also impartaesthetically pleasing components, such as fragrances and colorants intothe system. An illustration of such a system is the treatment offlushing toilets with automatically dispensed sanitizing, cleansing, andbacteriostatic agents to effectively clean and sanitize the toilet bowlwith every flush. From an aesthetic standpoint, it has been founddesirable to dispense fragrances and colorants at the same time, toimpart pleasing fragrance to the environment. The colorants not onlyimpart a pleasing appearance to the water in the toilet bowl, but theymay also serve to assure the consumer that, in fact, the desiredtreating agents (which are normally colorless) are being dispensed. Thecolorants may also serve as an indicator that the dispensing package hasbeen exhausted, i.e., their absence indicates the necessity for renewingthe treatment agents.

Most fragrances are hydrophobic in nature and are ordinarily formulatedand/or preserved in organic hydrocarbon bases. These "oily, waxy" basesare also hydrophobic and only contribute to the aqueous insolubility ofthe fragrance oils.

On the other hand, the systems of interest are aqueous in nature, and ittherefore becomes a problem to assure uniform and steady dispersion ofthe fragrance and, very often, the colorant components on a continuingbasis throughout the aqueous medium.

Heretofore, the dispensing of the water immiscible components into theaqueous medium has been solved by providing separate reservoirs for theimmiscible components. These reservoirs have been provided with sometype of valving arrangement to meter predetermined quantities of theimmiscible components into the aqueous medium during periods of aqueousflow or agitation. Upon release, the immiscible components arephysically carried along with the water flow, float to the surface atquiescent portions of the system, where they are released or evaporatedinto surrounding environment.

Such separate reservoir, valving arrangements suffer from a number ofpotential defects. First, since the immiscible component is released ona "shot by shot" basis, sufficient material must be released on each"shot" to ensure that enough material is delivered to the system toprovide the desired component at remote locations from the reservoirvalve location. This requirement demands release of a certain quantityof component at each operation of the valve. The mechanics of thisoperation, frequently requires the release of excess quantitites of thecomponents and the provision of relatively large reservoirs. Thisprocess also tends. to be inefficient and often requires the release oflarger "shots" of component than necessary to accomplish the job.

Secondly, the intermittent operation of the valves requires some type ofsensing mechanism to ensure valve operation at the proper time. Suchsensing mechanisms and the valves themselves are subject to failure orfaulty operation.

Thirdly, since sophisticated sensing and valve mechanisms are costly,there is a tendency to use the less precise and less complicatedmechanisms, whereby, close control of the amount of immiscible componentis unable to be maintained. The result is poor control over the uniformrelease of the immiscible components; and attendant greater use ofcomponents than is necessary for optimum results.

Thus it is apparent that there is a need for a simple reliable mechanismthat will deliver closely controlled amounts of immiscible materialsinto an aqueous system.

BRIEF DESCRIPTION OF THE INVENTION

The present invention utilizes silica-silicate foams to facilitate thedelivery of immiscible components into aqueous systems in a controlledmanner with excellent efficiency and reliability. The immisciblecomponents are adsorbed onto the foam and trapped within the voids whichare inherent to the foam's structure. Silica-silicate foams arewater-soluble, and as the foam dissolves when contacted with an aqueoussystem, the adsorbed and trapped immiscible components are released.

Although the foams are water-soluble it is important to note that theirsolubility is inherently lowered when the immiscible components areadsorbed thereon. That is, the ordinary low water solubility of the foamis greatly decreased and retarded by the presence of the adsorbedcomponents coating the foam surfaces. Thus there is a synergistic effectof prolonging the dissolution of the silica-silicate foam in the aqueousenvironment and the concommitant prolonged release of the immisciblecomponents into the same system.

The rate of release of the immiscible components is also controlled byseveral characteristics of the foam composition. Variations in thesilica to silicate ratios affects the rate of solubility of the foam inwater; and the density of the foam also affects the rate of dissolutionin the aqueous environment. Therefore, proper selection ofsilica-silicate ratios, foam density and the immiscible componentsthemselves determine the rate of release of the immiscible componentsinto the aqueous system.

More specifically, finely divided silica and silicate solution,preferably sodium silicate, are mixed together with added water to forma gel-like composition. This gel is then subjected to heat energy, suchas from a microwave generator. Under the influence of the energy input,water is driven from the silica-silicate reaction product and thesilica-silicate product swells, foams and solidifies into a porous,rigid solid.

The solid foam is then impregnated with a liquid solution of the desiredimmiscible component, ordinarily comprising organic components dissolvedin an oil, or an oil-like base. The organic component-oil solution isadsorbed onto the silica-silicate and additional quantities thereof aretrapped within the voids throughout the foam structure.

The impregnated foam product may then be placed in an aqueous system,whereupon the foam is gradually dissolved and the accompanyingimmiscible components are slowly and evenly released into the aqueoussurroundings.

The silica-silicate foam is especially useful in regulating the slow andprolonged release of fragrance oils into an aqueous system in which suchfragrance oils are normally immiscible.

It is therefore an object of the invention to provide a silica-silicatefoam impregnated with water immiscible components.

It is another object of the invention to provide a method for the slowand prolonged release of immiscible components into an aqueous system.

It is still another object to provide a method for the slow andprolonged release of immiscible fragrance oils into an aqueous system.

It is yet another object of the invention to provide a silica-silicatefoam impregnated with water immiscible organic components and to immersesaid impregnated foam over extended periods of time in an aqueousenvironment whereby said foam slowly dissolves and thereby releases theorganic components into the environment over said extended time periods.

Other objects and advantages of the invention will become apparent froma review of the following disclosure and the claims appended hereto.

DETAILED DESCRIPTION OF THE INVENTION

A rigid, water soluble foam is produced from mixing together suitablequantities of finely divided silica and sodium silicate solution, alongwith added water, if necessary, to form a gel, or gel-like product. Thesilica-silicate gel is then strongly heated, as by means of microwaveenergy, to drive off a quantity of the water. As the water is drivenoff, the gel expands (intumesces) and hardens to form the desired foam.

More specifically, silica, which is silicon oxide, SiO₂, is secured fromany of a number of industrial souces as a very fine anhydrous powder.Such sources are, for instance, the Cabot Corporation, of Boston, Mass.;or the Philadelphia Quartz Corporation of Valley Forge, Pa. The silicapowder is a standard article of commerce commonly used in themanufacture of glass, ceramics, refractories, abrasives, enamels; forthe decolorizing and purification of oils, and other petroleum products;and as a component in scouring and grinding compounds, ferro-silicon,and as casting molds. The powder has an extremely low coefficient ofexpansion by heat; and is essentially insoluble in water or acids, withthe exception of hydrofluoric acid.

The standard commercial product, which can be obtained in very highpurity, i.e., essentially 100% SiO₂, is entirely suitable for use in thepresent invention.

The sodium silicate is the reaction product of sodium oxide, Na₂ O, andsilica. It is available either as an aqueous solution, or as a powderedproduct. The sodium silicate component of the gel is a standard articleof commerce and may readily be obtained from several sources, e.g., thePhiladelphia Quartz Corporation of Valley Forge, Pa. While powderedsilicate may be used to prepare the gel, it is much more economical andconvenient to use aqueous solutions of sodium silicate. These aqueoussolutions are obtainable in varying composition with respect to theratio between sodium and silica, as well as in various densities. Thesolution, for instance, which is most commonly available contains about40% by weight Na₂ Si₃ O₇. If desired, other silicate solutions, such asNa₂ SiO₃, or Na₆ Si₂ O₇ may also be utilized. The desired properties,i.e., solubility, foam density, etc. of the final foam product, willgenerally determine the particular silicate solution utilized as astarting material.

As will be discussed hereafter, the physical and chemical properties ofthe silica-silicate foam depends, in great measure upon the ratios ofsodium oxide (Na₂ O), Silica (SiO₂), and water present in the gel beforethe heating procedure. An improper balance will result in weak, friablefoams, which quickly disintegrate when placed in the aqueous systems; orheavy foams of poor porosity that are incapable of adsorbing sufficientquantities of the immiscible component. Thus the particular silicatesolutions utilized are selected with consideration for the properties ofthe foams resulting from their use.

In any event, silica powder is slowly added with stirring to theselected silicate solution along with a sufficient amount of deionizedwater to produce a gel, or gel-like product. The viscosity of theresulting gel is determined by the original viscosity of the silicatesolution, by the amount of silica powder added, and by the amount ofwater added. The viscosity of the gel product increases with increasingsilica; but decreases with increasing water. Thus it will be readilyapparent that the final viscosity of the gel product can be easilycontrolled by varying the amounts of silica and water added to thesilicate solution.

In order to produce a final foam product of sufficient strength toresist damage when handled, and at the same time of sufficient porosityto adsorb and retain the desired amounts of the organic components, ithas been determined that gels having a composition of about 70-75% byweight water, about 20-25% by weight silica, and about 3-5% by weightsodium silicate, are necessary. In the instance where fragrance oils areto be adsorbed, it is desirable for the resultant foam to about 70 to80% by volume porosity. In order to resist crushing and damage and tomaintain its integrity during the extended period when being dissolvedin the aqueous systems, it is also desirable that the foam productexhibits a minimum crushing strength of about 9-10 kg/cm². The abovenoted proportions of water, silica, and silicate, along with a final gelviscosity of about 12 to 20 Mcps., will produce foams of the requiredporosity and crush strength.

It will be understood that, under certain circumstances, e.g., the useof different immiscible components, or in an environment where theassurance of extended release of the immiscible component is not socritical, the foam strengths and porosities may be varied considerablyfrom those which have been found to be desirable for the controlled,prolonged release of fragrance oils.

The gel is placed in a suitable mold within a microwave oven. Power isthen applied, whereupon microwave energy is directed into the gel mass.Good energy coupling is achieved due to the presence of water. Dependingupon the amount of gel present, microwave energy inputs in the 900 to3000 watt range are sufficient to drive off water at a rate to cause thegel to foam up and expand to many times its initial volume and formextensive voids within the mass.

Heating is continued until good foam growth is observed. Perhaps some 80to 90% or more by weight of the water originally present in the gel isdriven off during the heating process. The resultant rigid, porous foamis then removed from the microwave oven and is allowed to cool. It isthen ready for impregnation with the immiscible component.

The preferred foam has a porosity of at least 70% by volume or betterwith an open cell structure. That is, the voids should be open one tothe other and not closed. The presence of an appreciable quantity ofclosed cells is undesirable.

As noted above, foams with a crush strength of about 9-10 Kg/cm² aresatisfactory for use.

The immiscible components are loaded into the silica-silicate foam in arelatively simple method. The objective is to saturate the foam and fillthe void spaces completely as possible with the immiscible components.As noted above, the immiscible components are in the liquid form andconstitute a hydrophobic oily base in which the active components, suchas fragrances or dyes are dissolved. Such materials generally have theviscosity of light mineral oils with a viscosity somewhat higher thanwater, but still quite fluid.

To ensure complete saturation of the silica-silicate foam, a vacuumprocedure is appropriate. Specifically, the silica-silicate foam, in theform of blocks, is placed in a vacuum chamber equipped with suitablepiping and valve means to afford the introduction of the immiscibleliquid materials when desired. A mild vacuum is pulled on the foamblocks to reduce the air pressure within the voids. The liquidimmiscible materials are then valved into the chamber to a levelsufficient to cover the foam blocks. The chamber is then let up toatmospheric pressure and the immiscible components are thereby forcedinto the interior voids of the silica-silicate foam.

After a time sufficient to ensure thorough saturation of the foam, theblocks are removed from the vacuum chamber, and placed on a poroussurface to permit drainage of the excess immiscible liquid. The foam isthoroughly "wet" by the immiscible components and the voids aresaturated therewith. At this time the impregnated foam is ready for use,or the blocks can be sealed in a closed package until ready for use.

When desired, the impregnated foam blocks may be placed in the aqueoussystem into which the immiscible components are to be dispensed. Atypical system is the tank compartment of a toilet where it is desirableto dispense disinfecting and/or detergent materials, as well asfragrances and to indicate the presence of the disinfectants/detergentsin the flush water. The foam product may be utiized in conjunction withmeans to dispense disinfecting and/or detergent materials into thesystem, however, such disinfectant/detergent dispensing means forms nopart of this invention.

The impregnated foam block, however, may be packaged along with thedisinfecting/detergent materials as a unitary package; or it may bepackaged separately from the disinfecting and detergent components. Inany event, the impregnated foam block is placed within the tankcompartment into contact with the flush water.

When in contact with the aqueous environment, the foam is subjected tothe solvent action of the water. A silica-silicate foam having thetypical chemical and physical characteristics noted above, whenunimpregnated with the oily immiscible components will readilydisintegrate and dissolve in the aqueous environment in a matter of afew hours. However, when impregnated with oily immiscible components,the dissolution and disintegration is drastically retarded and isextended to days or several weeks. Even more surprisingly, when thesilica-silicate foams are impregnated with fragrance oils, thedissolution is even further extended to the order of several months.

For instance, utilizing identical size pieces of silica-silicate foamprepared from gels of identical composition and utilizing the sameheating parameters, it has been noted that the unimpregnated foamsdissolve and disintegrate in a matter of a day or two. When the foamswere impregnated with a light hydrocarbon oil, disintegration occurredin a matter of several weeks. However, when the foams were impregnatedwith a fragrance oil e.g. Firminich disintegration was delayed for eightweeks and even longer. It should be understood that, in all instances,the foams disintegrated and dissolved. But in the instance ofimpregnation with immiscible fragrance oils, dissolution was delayed.Even though the foam decreased in size during dissolution, the remainingfoam maintained its integrity.

It is believed that the extended dissolution and maintenance ofintegrity of the fragrance oil impregnated foams can be explained on thefollowing basis:

Fragrance oils almost universally include functional groups which arecapable of forming polar bonds. These polar functional groups thereforehave the ability to associate rather strongly with the silica-silicatestructure. When adsorbed on the silica-silicate surfaces the polargroups are associated strongly thereto, and the hydrophobic functionalgroups form a layer which protects the silica-silicate from readycontact with the water molecules which would dissolve thesilica-silicate.

Eventually the fragrance oils slowly dissipate into the aqueousenvironment through diffusion. At any point of exposure, the silicatestructure is attacked and dissolved by the water with attendantdisintegration of the silica-silicate structure and additional releaseof the immiscible fragrance oils.

While the above explanation is believed to account for the increasedstability of the silica-silicate foams impregnated with water immisciblepolar compounds, its veracity is unsubstantiated and the explanationshould be considered as theory only. In fact, however, tests haveclearly shown that the integrity of silica-silicate foams is prolongedin an aqueous environment when the foams are impregnated with fragranceoils.

As a consequence of the increased life of the foams, the release offragrance oils into the aqeuous system is also prolonged over times farlonger than normally expected from the amounts of fragrance oilsutilized.

Dyes may also be added to the immiscible components to indicate therelease therewith as the silica-silicate foams dissolve. The dye will bereleased at the same time the immiscible component is released. Thus theflush water will be dyed to indicate the presence of the desireddisinfectants and/or detergents, when the release of the immisciblecomponents is coordinated with release of the disinfectants/detergents.

Suitable fragrance oils for use in the invention are:

Citronellol, hydroxycitronellol, rhodinol, eugenol, geraniol, rose oil,heliotropine, peru balsam, ylang-ylang oil, isoeugenol, bergamot,coumarin, and any of the synthetic counterparts or blends of theforegoing, and odorant chemicals of which there is no counterpart innature. Any or all of these materials may be used in combination toachieve any desired fragrance and odor counteractant effect.

Some fragrance oils found to be particularly useful in toilet flushingaqueous systems are: An herbal scent, Firminich 43.312/B; a fantasyscent, Firminich Cetylia Base®; a lemon scent, Naarden 802605; and apine scent, Synfleur C-78-132.

Suitable dyes for admixing with the fragrance oils are:

Acid Blue #9 (preferred); Acid Blue #1; Acid Blue #7; and Acid Blue #86.

As noted above, microwave energy is the preferred means of driving waterfrom the silica-silicate gels. Microwaves will heat the gel throughoutits entire mass virtually simultaneously, thus driving off water fromthe interior portions of the gel mass as well as from the exteriorportions thereof. A uniformly open-celled fine foam structure may betherefor obtained.

The following examples will further illustrate various aspects of theinvention:

EXAMPLE 1

The following table presents chemical and physical properties fromtypical experimental foam preparations:

                  TABLE I    ______________________________________    Sample #    ______________________________________           Composition of           Gel % W           Water Silica  Na.sub.2 O                                 Gel Viscosity Mcp.    ______________________________________    A        75      21.6    3.4   17.6    B        75      20.7    4.3    5.7    C        75      20.7    4.3   --    D        70      25      5     10.6    ______________________________________             Porosity % V    Strength, Kg/cm.sup.2    ______________________________________    A        79              13.9    B        78              17.8    C        76              11.5    D        77               8.6    ______________________________________

EXAMPLE 2

A silica-silicate foam tablet was prepared according to the abovedescription. The tablet was impregnated with 30% by weight of thefragrance oil Cetylia, from Firminich. The impregnated tablet was placedinto a laboratory flush system along with a quantity of calciumhypochlorite. As the system was repeatedly flushed, both thehypochlorite and the foam gradually dissolved into the water in thebowl. The hypochlorite, of course, normally gives a typical "chlorine"odor and the system was observed to determine if the released fragranceoil would mask the "chlorine" odor. After 100 flushes in whichhypochlorite reached levels equivalent to 1.5 ppm chlorine, the Cetyliaoil continued to strongly mask any "chlorine" odor. The remaining foamtablet was also intact and fragrance was still being released into thesystem.

I claim:
 1. A method of producing a water soluble foam structure from anaqueous gel including silica-silicate and about 70 to 75% by weightwater comprising driving a portion of said water off from the aqueousgel by applying microwave energy to said gel to thereby produce a foamedstructure.
 2. A silica-silicate gel for use in producing a foamedstructure comprising from about 70 to 75% by weight water, from about 20to 25% by weight silica, and from about 3 to 5% by weight sodiumsilicate.
 3. The silica-silicate gel by claim 2 having a viscosity ofabout 12 to 20 Mcps.